--- a/vmcore-dmesg/vmcore-dmesg.c
+++ b/vmcore-dmesg/vmcore-dmesg.c
@@ -1,6 +1,8 @@
 #define _XOPEN_SOURCE 600
 #define _LARGEFILE_SOURCE 1
 #define _FILE_OFFSET_BITS 64
+#define _GNU_SOURCE
+
 #include <endian.h>
 #include <byteswap.h>
 #include <stdio.h>
